1. Technical Field
This invention relates to vane pumps.
2. Related Art
A vane pump typically includes a cylindrical rotor supported for rotation inside of an oval-shaped rotor chamber defined by a cam ring surrounding the rotor. The cam ring and the rotor define crescent-shaped cavities therebetween which are divided in to a plurality of pump chambers by a corresponding plurality of flat vanes carried in radial vane slots of the rotor. The pump chambers expand into an inlet sector of the crescent-shaped cavities and collapse in a discharge sector of the cavities as the rotor rotates. A thrust plate and a pressure plate are disposed on opposite sides of the cam ring and are squeezed together under spring tension to cover the rotor chamber. An opposite thrust face of the thrust plate is pinned between the cam ring and end wall of the housing. A significant fluid pressure differential is developed across the thrust plate which induces flexure of the thrust plate away from the rotor toward the end wall. A clearance dimension between the housing, thrust plate, and rotor calculated to accommodate such flexure exceeds a corresponding clearance dimension needed for high volumetric efficiency. Fluid leakage from the pump chambers attributable to the extra clearance for flexure of the thrust plate reduces the volumetric efficiency of the vane pump.
U.S. Pat. No. 6,050,796 discloses a vane pump having a hydraulically balanced rotor for improving the efficiency of the pump. The present invention provides further improvements to vane pumps.
A vane pump constructed according to the invention comprises a pump housing having a longitudinal axis, a cavity for hydraulic fluid, and a substantially planar end wall of the housing which is exposed to the cavity. A thrust plate is disposed in the cavity having a first thrust face disposed in adjacent facing relation to the end wall of the housing, and an opposite second thrust face. The thrust face has at least one fluid inlet port communicating with the cavity. A pressure plate is disposed in the cavity in axially space relation to the thrust plate. A cam ring is disposed in the cavity between the thrust plate and pressure plate and has a circumferentially extending inner cam wall defining a rotor chamber of the cavity. A rotor is supported in the rotor chamber for rotation about the longitudinal axis of the housing relative to the inner cam wall of the cam ring. A plurality of vanes are slideably supported by the rotor for radial reciprocation in communication with the inner cam wall of the cam ring to define a plurality of dynamically expanding and diminishing volume sectors of the rotor chamber and which are operative to draw hydraulic fluid into the rotor chamber under low pressure and expel the hydraulic fluid under elevated pressure from the rotor chamber. A resilient gasket is disposed between the first thrust face of the thrust plate and the end wall of the housing to define a sealed balance chamber therebetween.
Provision of the balance chamber is operative to exert counteracting controlled fluid pressure on the first thrust face to oppose the fluid pressure exerted on the second thrust face so as to support the thrust plate in hydraulic equilibrium within the pump housing. The balance of fluid force on axially opposite sides of the thrust plate minimize or eliminate thrust plate flexure away from the rotor, allowing for tighter dimensional tolerance of the thrust plate and rotor which in turn lessens leakage of high pressure fluid past the thrust plate and lessens the loss of volumetric efficiency associated therewith. When combined with a hydraulically balanced rotor, a pump constructed according to the invention has been shown to improve volumetric efficiency by as much as 57% over traditional vane pumps without such balanced thrust plate and rotor components.